1.Calculate the weight average molecular weight for a thermoplastic that has the following weight fractions for the molecular weight ranges listed.Hint: consult pages17and 18 of lecture file 210426.Molecular Weight Range(g/mol)Weight FractionMolecular Weight Range(g/mol)Weight Fraction0 –5,0000.0120,000 –25,0000.195,000 –10,0000.0425,000 –30,0000.2110,000 –15,0000.1630,000 –35,0000.1515,000 –20,0000.1735,000 –40,0000.072.The average molecular weight of a random poly(isobutylene–isoprene) copolymer is known to be 77,630 g/mol with a degree of polymerization of 1250.
(a) Determine the number fraction of each of the two components. (b) Which type(s) of copolymer(s) will this copolymer be, considering the following possibilities: random, alternating, graft, and block? Why?
3.Compute the weight percentsulfur that must be added to completely crosslink an alternating acrylonitrile–butadiene copolymer, assuming that four sulfur atoms participate in each crosslink.
4.A polymer material, subjected to a constant strain of 0.5, undergoes stress relaxation from 3.5 MPa to 0.5 MPa in 30 seconds. What is its modulus of elasticity at 10 second?
5.Consider a unidirectional Kevlar 49–fiber–epoxy composite material containing 63 percent by volume of Kevlar 49 fibers. Calculate
(a) density,
b) modulus of elasticity under isostrain condition, and
(c) modulus of elasticity under isostress condition.MaterialDensity (g/cm3)Modulus of Elasticity (GPa)Kevlar 491.44207Epoxy Resin1.204.50
6.A unidirectional carbon–fiber–epoxy–resin composite contains 65 percent by volume of carbon fiber and 35 percent epoxy resin. Calculate for the composite
(a) the average density,
(b) the weight percentages of carbon fibers and epoxy,
(c) the maximum possible tensile modulus of elasticity,
(d) the minimum tensile modulus of elasticity,
(e) the maximum tensile strength, and
(f) the fraction of the tensile load carried by the carbon fibers.MaterialDensity (g/cm3)Modulus of Elasticity (GPa)Tensile Strength (MPa)Carbon Fiber1.793402140Epoxy Resin1.204.5064
